Crystal pulling method and apparatus for the practice thereof

Abstract

A method and an apparatus are proposed for pulling crystals from the melt. The recharging of the melt (4) is performed such that the crucible (3) is raised and lowered with respect to the crystal pulling system while keeping the position of the melt surface (25) constant with respect to the crystal pulling system. In particular it is proposed that, during a first time interval (34) the amount of recharge (37) per unit time be greater than the average amount of recharge (38, 39) per unit time that would be necessary in order to make up for the consumption of material by the growing crystal (5), that during a second time interval (45) the amount of recharge (46) per unit time be less than the average recharge amount per unit time that would be necessary in order to make up for the consumption of material by the growing crystal, that during the first time interval the crucible (3) be lowered to keep the melt surface constant with respect to the crystal pulling apparatus, that during the second time interval the crucible (3) be raised to keep the melt surface constant with respect to the crystal pulling apparatus. By the invention, erosion ring grooves on the inside wall of the crucible are prevented and thus the useful life of the crucible is considerably lengthened. The method according to the invention can be practiced on existing apparatus.

I claim: 
     
       1. Method for pulling crystals from the melt, comprising: utilizing a crystal pulling apparatus which has a device for measuring the position of the surface of the melt during the pulling process, a charging device for recharging the melt during the pulling process, a positioning device for positioning the crucible during the pulling process, and performing the recharging such that, with the position of the melt surface constant with respect to the crystal pulling apparatus, during a first time interval (34) a recharge amount (37) per unit time is greater than an average recharge amount (38, 39) per unit time that would be necessary in order to make up for material consumption by a growing crystal (5), and in which during a second time interval (45) a recharge amount (46) per unit time is smaller than the average recharge amount (38, 39) per unit time that would be necessary in order to make up for the material consumption by the growing crystal (5), and which includes during the first time interval (34), to keep a melt surface (25) constant with respect to the crystal pulling apparatus, lowering the crucible (3) and which includes during the second time interval (45), to keep the melt surface (25) constant with respect to the crystal pulling apparatus, raising the crucible (3).